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ESA1 - Physiology and Pharmacology > Pharmacodynamics > Flashcards

Pharmacodynamics Flashcards

1
Q

How do drugs exert effects?

A

By binding to a target - usually a protein

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2
Q

What is an example of a b2-adrenoceptor agonist?

A

Salmeterol - used in asthma treatment

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3
Q

What does adalimumab treat?

A

Rheumatoid arthritis

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4
Q

What is critical in determining drug action?

A

Concentration of drug molecules around receptors

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5
Q

What is pharmacodynamics?

A

Study of how drug effects the body

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6
Q

What is a ligand?

A

A molecule/ion that binds to another molecule (usually a receptor)

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7
Q

What is the difference between affinity and efficacy?

A 
Affinity = how easily it binds
Efficacy = how effective it is when bound
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8
Q

What is an agonist?

A

A substance which initiates a physiological response when combined with a receptor.

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9
Q

What is an antagonist?

A

A substance which interferes with or inhibits the physiological action of another.

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10
Q

What are partial agonists?

A

Drugs that bind to and activate a given receptor, but have only partial efficacy at the receptor relative to a full agonist.

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11
Q

What is intrinsic activity?

A

Intrinsic activity or efficacy refers to the relative ability of a drug-receptor complex to produce a maximum functional response

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12
Q

What is functional antagonism?

A

An antagonist may act at a completely separate receptor, initiating effects that are functionally the opposite of the agonist.

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13
Q

What is a competitive antagonist?

A

A competitive antagonist is a receptor antagonist that binds to a receptor but does not activate the receptor.

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14
Q

What is a non-competitive antagonist?

A

A non-competitive antagonist binds to an allosteric site on the receptor to prevent activation of the receptor

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15
Q

What is the equation for molarity?

A

Molarity(M) = g/L
——
MWt

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16
Q

Why do we need to consider drug concentrations in molarity, as opposed to weight?

A

Different concentrations of molecules and this is critical in determining drug action

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17
Q

What is drug binding governed by?

A

Association and dissociation

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18
Q

What does an agonist binding to a receptor cause?

A

Conformational change

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19
Q

What do agonists have compared to antagonists?

A

Agonists have intrinsic efficacy (can activate receptor) and efficacy (cause measurable response) while antagonists have affinity only (cannot activate receptor)

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20
Q

Why don’t antagonists cause a response?

A

They lack intrinsic efficacy

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21
Q

How do we measure drug-receptor interactions by binding?

A

Binding a radioactively labelled liand to cells o membranes prepared from cells.

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22
Q

What is Bmax?

A

Maximum binding capacity - no receptors left

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23
Q

What is Kd?

A

Concentration of ligand required to occupy 50% of the available receptors

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24
Q

What does a lower Kd value mean in terms of affinity?

A

Lower value = higher affinity

Kd is actually the reciprocal of affinity

25
If drug A has a Kd of 1nM and drug B has a Kd of 1mM, which has higher affinity?
Drug A - lower concentration required occupy 50% of receptors
26
When the concentration of a drug is expressed linearly, what is the shape of the graph showing the relationship between [drug] and proportion of bound receptors?
Rectangular hyperbola
27
When the concentration of a drug is expressed logarithmically, what is the shape of the graph showing the relationship between [drug] and proportion of bound receptors?
Sigmoidal
28
For example, what is -9(log10)M?
10^-9 M
29
What could the response generated by a drug be?
Change in signalling pathway, change in cell or tissue behaviour (e.g. Contraction)
30
What is EC50?
Effective concentration giving 50% of maximal response
31
What is EC50 a measure of?
Potency
32
How does dose differ from concentration?
Concentration = known concentration at site of action Dose = concentration at site of action is unknown eg dose to a patient in mg or mg/kg
33
What does a ligand require to have potency?
1) ligand binding to the receptor (affinity) 2) receptor activation (intrinsic efficacy) 3) things to happen to generate a measurable response Affinity + efficacy = potency
34
Why do you need selective/specific activation of b2 adrenoceptors in the airways to treat asthma?
Other b-adrenoceptors such as b1 in the heart which would increase force and rate
35
What is the Kd of b1 adrenoceptors to salbutamol as apposed to b2 adrenoceptors and what does this mean?
B1 Kd - 20 micromoles B2 Kd - 1 micromole B2 receptors have a lower Kd (20 fold) so a higher affinity.
36
How is salbutamol usage enhanced?
By b2 selective efficacy and route of administration
37
What is the Kd of b1 and b2 adrenoceptors to salmeterol and what does this mean?
B1 Kd - 1900nM B2 Kd - 0.55 nM B2 lower Kd so higher affinity - very selective (3455 fold) But no selective efficacy, selectivity based on affinity
38
Why is response controlled or limited often?
Eg muscles can only contract so much, glands can only secrete so much
39
In some cases <100% occupancy = 100% response. What is this due to?
Spare receptors
40
When are spare receptors often seen?
When receptors catalytically active eg GPCRs or tyrosine kinase
41
Why do spare receptors exist?
- Amplification in the signal transduction pathway | - Response limited by a post-receptor event eg contraction
42
For example, in the parasympathetic stimulation of M3 receptors, what percentage of receptors need to be occupied for maximal contraction of the airway smooth muscle?
10% | - so 90% appear to be spare receptors
43
Why have spare receptors?
Increase sensitivity so allow responses at low concentrations of agonist
44
Are receptor numbers fixed?
No Tend to increase with low activity (up-regulation) and decrease with high activity (down-regulation [for drugs this can contribute to tolerance/tachyphylaxis])
45
Why do partial agonists have lower intrinsic activity?
They have lower efficacy than full agonists
46
What is the relevance of partial agonists?
They can allow a more controlled response, work in the absense of/low levels of ligand and act as an antagonist if there are high levels of full agonist
47
What are examples of partial agonists?
Opiods - pain relief, recreational Action through mu-opiod receptor Can lead to death as respiratory depression
48
Why can buprenorphine be adventageous to morphine in some clinical settings?
Heroin - full agonist, Buprenorphine - partial agonist adequate pain control, less respiratory depression as lower Kd and lower efficacy
49
Are partial agonists ALWAYS partial agonists?
No - compound and system dependent so increasing receptor number can change a partial agonist into a full agonist
50
Do full or partial agonists have a lower efficacy?
Partial
51
What is IC50?
Index of antagonist potency determined by strength of stimulus
52
What is an example of a high affinity, competitive antagonist at mu-opiod receptors?
Naloxone - reversal of opioid mediated respiratory depression - high affinity means it will compete effectively with other opiods
53
What are competitive antagonists also known as?
Surmountable angtagonists
54
What shift in a graph do reversible competitive antagonists cause?
Parallel shift to the right of the agonists concentration-response curve
55
What are irreversible competitive antagonists also known as?
Non-surmountable
56
What shift in a graph do irreversible competitive antagonists cause?
Parallel shift to the right of the agonist concentration-response curve and at higher concentration suppress the maximal response
57
What is an example of an irreversible competitive antagonist?
Phenoxybenzamine - non selective irreversible a1 blocker used in hypertension episodes in pheochromocytoma Clopidogrel (plavix) - P2Y12 antagonist to reduce thrombosis/risk of heart disease - it is a prodrug so needs cytochrome P450 metabolism
58
What do allosteric sites provide binding for?
Agonists | Moleculs that enhance or reduce effects of agonists (eg non competitive antagonism)

ESA1 - Physiology and Pharmacology (11 decks)

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